Tornado Risk

Understanding Tornado Risk on SPC Convective Outlooks

When the Storm Prediction Center (SPC) issues severe weather outlooks, they don’t just say if storms are possible — they quantify tornado threat with numbers and sometimes special symbols. For anyone tracking severe weather, understanding these elements helps you go beyond “yellow on a map” to what it really means for your location.

What Do Tornado Percentages Mean?

On Convective Outlook graphics, you’ll often see tornado probabilities expressed as percentages for an area:

• These percentages represent the chance that a tornado will occur within 25 miles of any given point in that shaded area during the outlook period. That’s roughly the size of a typical metropolitan area.

• For example, a 15% tornado probability does not mean a tornado is certain — but it does mean there’s a 15% chance of a tornado within 25 miles of your location. That is significantly higher than climatological odds (on most days your chance is near zero), so even seemingly modest percentages represent a meaningful threat that should be taken seriously.

• Lower percentages (e.g., 2–5%) indicate a lower chance of tornadoes, but not zero — even “slight risk” days can produce tornadoes, especially isolated ones.

The SPC uses these numbers in probabilistic outlooks that help forecasters and emergency managers anticipate where storms are most likely to produce tornadoes, damaging winds, or hail.

What Is a “Hatched Risk Area”?

You might also see areas on a tornado outlook filled with diagonal lines, cross-hatching, or otherwise “hatched.” That’s more than just decoration — it carries extra meaning:

• A hatched tornado outlook area means there’s a relatively higher risk of significant tornadoes — typically tornadoes at least EF2 strength or stronger — within 25 miles of any point in that zone.

• In other words, a hatched probability isn’t just about the likelihood of any tornado occurring, it indicates the environment may be favorable for stronger tornadoes with more destructive potential.

• Hatched areas are relatively uncommon and signal that forecasters see parameters that could support tornadoes capable of producing more significant damage if they occur.

Putting It Together

Understanding tornado outlooks is less about a single number and more about the forecast message:

• Higher tornado probabilities mean tornadoes are more likely near you — even

  mid-teens percentages are noteworthy because typical daily tornado risk is so low.

• A hatched risk elevates the concern to the possibility of stronger tornadoes.

• These outlooks help emergency managers and the public prepare before watches or warnings are issued by indicating where severe weather hazards are most favored.

Put simply: if you’re in a non-hatched risk area with a moderate tornado probability, expect some chance of a tornado. If you’re also in a hatched area, the environment may support more intense, damaging tornadoes — and your readiness posture should reflect that.